We are developing an in vitro human mammary cell culture system to be used for studies of human cellular differentiation and carcinogenesis. In particular, we will investigate: (1) the effects of potential growth promoters on human mammary epithelial cell; (2) the effects of hormones and cell substrates on expression of mammary-specific products (medium chain fatty acids, gamma-lactalbumin, casein); (3) properties that may differentiate between normal and malignant mammary epithelial cells (surface properties, tumor-specific antigens); and (4) metabolism of benzo-a-pyrene by these cells.